The present invention relates to thrust bearings for turbochargers.
In FIG. 1 is shown in side view, partly in section, a prior art turbocharger. In operation, the back pressures of a blower impeller b and a turbine wheel c which are carried by a common shaft a vary depending upon the rotational speed and the operating range; that is, the back pressures fluctuate between the positive and negative pressures. As a result, the common shaft is subjected to axial thrust. In order to prevent the axial motion of the common shaft a due to such thrusts, as shown in detail in FIG. 2, a thrust metal d is rigidly secured to a bearing casing g so as to be sandwiched or interposed between an oil thrower e and a thrust bushing f both carried by the common shaft a so that the thrust metal d carries the thrust loads. With the arrangement as shown in FIG. 2, it is difficult to satisfactorily lubricate the thrust-load carrying interfaces h and h'. As a consequence, oil films, are frequently fractured, resulting in seizure between the thrust metal d on the one hand and the oil thrower e and the thrust bushing f on the other hand. Furthermore, the temperatures of lubricating oil in the interfaces h and h' rise exceedingly. Therefore the thrust bearing of the type just described above has a low load carrying capacity. To overcome this problem, lubricating oil must be circulated in large quantities, but only a small portion of lubricating oil serves to lubricate the interfaces h and h', whereas the remaining lubricating oil merely flows through the interfaces h and h' without effecting any effective lubrication. It follows therefore that flowing of lubricating oil in large quantities serves no lubrication purpose at all.
One of the objects of the present invention is therefore to provide a thrust bearing for a turbocharger in which the construction of a thrust metal is so modified that the overall quanitity of lubricating oil which is required can be reduced yet reliable and dependable operation can be ensured and furthermore the thrust-load carrying capacity can be remarkably increased.
Briefly stated, to the above and other ends, the present invention provides a thrust bearing for a turbocharger of the type having a thrust metal with a radial lubricating feed passage in communication with a lubricating oil supply port, a thrust bushing and an oil thrower, thrust-load carrying interfaces being defined by said thrust metal, said thrust bushing and said oil thrower, characterized in that it comprises an annular groove-like oil reservoir formed on an inner perpheral wall of the thrust metal, and at least a small-diameter hole extending axially into the thrust metal to make the annular groove-like oil reservoir communicate with the thrust-load carrying interfaces.
The above and other objects, features and advantages of the present invention will become more apparent from the description of a preferred embodiment thereof taken in conjunction with the accompanying drawings.